Magnetic Random-Access Memory (MRAM) is a non-volatile computer memory technology based on magnetoresistance. One type of MRAM cell is a spin torque transfer MRAM (STT-MRAM) cell, which includes a magnetic cell core supported by a substrate. The magnetic cell core includes at least two magnetic regions, for example, a “fixed region” and a “free region,” with a non-magnetic region in between. The free region and the fixed region may exhibit magnetic orientations that are either horizontally oriented (“in-plane”) or perpendicularly oriented (“out-of-plane”) relative to the width of the regions. The fixed region includes a magnetic material that has a substantially fixed magnetic orientation (e.g., a non-switchable magnetic orientation during normal operation). The free region, on the other hand, includes a magnetic material that has a magnetic orientation that may be switched, during operation of the cell, between a “parallel” configuration and an “anti-parallel” configuration. In the parallel configuration, the magnetic orientations of the fixed region and the free region are directed in the same direction (e.g., north and north, east and east, south and south, or west and west, respectively). In the “anti-parallel” configuration, the magnetic orientations of the fixed region and the free region are directed in opposite directions (e.g., north and south, east and west, south and north, or west and east, respectively). In the parallel configuration, the STT-MRAM cell exhibits a lower electrical resistance across the magnetoresistive elements (e.g., the fixed region and free region). This state of low electrical resistance may be defined as a “0” logic state of the STT-MRAM cell. In the anti-parallel configuration, the STT-MRAM cell exhibits a higher electrical resistance across the magnetoresistive elements. This state of high electrical resistance may be defined as a “1” logic state of the STT-MRAM cell.
Switching of the magnetic orientation of the free region may be accomplished by passing a programming current through the magnetic cell core and the fixed and free regions therein. The fixed region polarizes the electron spin of the programming current, and torque is created as the spin-polarized current passes through the core. The spin-polarized electron current exerts torque on the free region. When the torque of the spin-polarized electron current passing through the core is greater than a critical switching current density (Jc) of the free region, the direction of the magnetic orientation of the free region is switched. Thus, the programming current can be used to alter the electrical resistance across the magnetic regions. The resulting high or low electrical resistance states across the magnetoresistive elements enable the read and write operations of the STT-MRAM cell. After switching the magnetic orientation of the free region to achieve the parallel configuration or the anti-parallel configuration associated with a desired logic state, the magnetic orientation of the free region is usually desired to be maintained, during a “storage” stage, until the STT-MRAM cell is to be rewritten to a different configuration (i.e., to a different logic state).
However, the presence of a magnetic dipole field emitted from the fixed region may impair the ability to symmetrically switch the magnetic orientation of the free region during operation of the STT-MRAM cell. Efforts have been made to eliminate the negative effects of switching due to interference from a stray magnetic dipole field. For example, magnetic materials including a synthetic antiferromagnet including an upper magnetic region and a lower magnetic region separated by a coupling material may reduce the negative effect of stray magnetic dipole fields. Each of the upper magnetic region and the lower magnetic region may include magnetic materials separated from each other by a conductive material. The coupling material is formulated and positioned to provide an anti-parallel coupling of adjacent magnetic materials. The goal is that a magnetic dipole field emitted by the upper region will be effectively canceled by a magnetic dipole emitted by the lower region due to the opposite directions of the respective magnetic orientations. However, magnetic coupling between the upper region and the lower region may exhibit oscillatory behavior between ferromagnetic coupling and antiferromagnetic coupling. Further, in conventional synthetic antiferromagnets, growth of the upper magnetic region may be limited by the type and thickness of the coupling material, whereas the magnetic characteristics (e.g., the PMA, the magnetic hysteresis, etc.) of the lower magnetic region may be determined by an underlying conventional seed material, that may include tantalum and ruthenium. For example, magnetic regions located farther from the seed material than other magnetic regions (e.g., magnetic regions that are distal from the seed material) may exhibit a crystalline structure that is different from the other magnetic regions and the seed material, which may cause the magnetic cell structure including the magnetic regions to exhibit structural defects and a reduced PMA.
Efforts to couple the coupling material to the upper and lower magnetic materials include annealing the coupling material and the upper and lower magnetic materials. However, while annealing may improve the crystal structure of the magnetic materials and improve the adhesion between the magnetic materials and the coupling material, annealing may reduce the magnetic properties (e.g., the magnetic anisotropy (“MA”) and the perpendicular magnetic anisotropy (“PMA”)) of the magnetic materials. Annealing may also affect the strength of the coupling between the magnetic materials and the coupling material which may affect the antiferromagnetism and/or the antiferromagnetism of the coupled magnetic structure. For example, annealing may alter the crystal orientation of the magnetic material and may create in-plane or out-of-plane magnetic moments that may interfere with reading and writing operations of the memory cell. Thus, annealing may reduce the PMA of the magnetic materials and may create out-of-plane magnetic dipole moments that interfere with operation of a magnetic cell structure incorporating the magnetic materials.